1. Field of the Invention
The present invention relates to a broadcasting signal receiving system capable of receiving broadcast signals transmitted in NTSC, PAL-M and PAL-N systems, and more particularly to an apparatus for automatically switching broadcasting systems capable of stabilizing a broadcasting signal receiving system and a controlling method of using the same.
2. Description of the Prior Art
Broadcasting systems of broadcast signals provided from broadcasting stations are generally classified into a SYSTEM M, B/G, D/K, I and L in accordance with the characteristics of transmitted signals, and classified into NTSC (National Television System Committee), PAL (Phase Alternation by Line) and SECAM (Sequential Couleur a Memoire) in accordance with the characteristics of color signals.
Broadcasting stations of respective nations send broadcast signals of combining a TV broadcasting system with a TV color system. For example, NTSC-M system is adopted by the United States, Japan, Korea, etc., and PAL-B/G system is by western European countries such as German, Spain, Italy and Sweden. PAL-D/K system is standard in China, Rumania, etc. England, Island and South Africa Republic adopt PAL-I system, and France and Luxemburg adopt SECAM-L system.
Eastern European countries such as United independence nations adopt PAL-M system (in which the number of scanning lines is 525 H, field frequency is 59.94 Hz and chrominance subcarrier frequency Fsc is 3.575611 MHz), and PAL-N (having 625 H/50 Hz and Fsc of 3.582056 MHz) is standard in Argentina. Therefore, when a user migrates to a region having a different broadcasting system, the broadcasting system of the television should be set again for receiving the broadcast signals of corresponding region.
Among the broadcasting systems of broadcast signals, NTSC system and PAL-M system have the identical vertical sync frequency set to 60 Hz, and PAL-N system has the vertical sync frequency set to 50 Hz. Thus, in a common television, the frequency of the vertical sync signal inserted into the broadcast signal is detected, the broadcasting system is set in accordance with the frequency of the detected vertical sync signal. Then, the chrominance subcarrier is oscillated in accordance with the set broadcasting system, and the broadcast signal is processed in accordance with the oscillated chrominance subcarrier.
For instance, in case that the frequency of the vertical sync signal included in the broadcast signal is 50 Hz, the broadcasting system is of PAL-N system. Therefore, the television oscillates the chrominance subcarrier corresponding to the broadcasting system, and processes the broadcast signal received via an antenna in accordance with the oscillated chrominance subcarrier.
Also, in case that the frequency of the vertical sync signal is 60 Hz, the broadcasting system is set to PAL-M in the television, and the broadcast signal is processed in accordance with the PAL-M system set as above. Once a color killer signal is generated from the processed broadcast signal, the broadcasting system is switched into the NTSC system, and the broadcast signal is processed in accordance with the NTSC system.
The conventional television in which the PAL-M system is set as a default system mutes a video signal in a region where the NTSC system is applied while the PAL-M system is switching into NTSC system. That is, the received broadcast signal is first processed in view of the PAL-M system. Then, once the color killer signal is generated from the processed broadcast signal, the received broadcast signal is processed in view of the NTSC system. The video signal is muted until the received broadcast signal is processed by the NTSC system. The muting time of the video signal is approximately 200ms! or so taken from turning on a power switch to displaying the video signal.
Several methods for automatically switching broadcasting systems for shortening the switching time from the PAL-M system to NTSC system have been suggested in recent years. However, when the electric power intensity of the broadcast signal transmitted from a broadcasting station is insignificant or broadcast signals interfere with each other during the transmission, a color burst signal included in the broadcast signal is lost and a color killer signal is detected in the broadcasting signal receiving system, e.g., television, VCR, etc.
In this case, even though the broadcast signal of the system identical to the default system (PAL-M system) is received, the broadcasting signal receiving system, processes the broadcast signal by switching it into the other broadcasting system (NTSC system) that is different from the default system set into the broadcasting signal receiving system.
Furthermore, when broadcast signals of different systems are recorded on a video tape, i.e., in the order of NTSC/PAL-M/monochrome/NTSC/ . . . , the color killer signal is continuously detected while the monochrome broadcast signal is detected, and the broadcasting signal receiving system should repeatedly switch the default system while the color killer signals is detected. Therefore, when the broadcast signal processed in the NTSC system is switched into the PAL-M system to be processed, the tint resulting from a color phase is displayed on a screen in case of processing the broadcast signal in the NTSC system. Also, when the broadcast signal is processed in the PAL-M system, an OSD (alphanumeric signal) flickers since the tint is not displayed. Consequently, a consumer wrongly considers it as a breakdown of the broadcasting signal receiving system. Additionally, the broadcasting signal receiving system under operation is internally unstable to be disadvantageous of shortening durability or degrading performance of the broadcasting signal receiving system.